Abstract Transcription of DNA into mRNA is only a first step in gene expression. The following phase, mRNA translation, is highly regulated and equally important in determining protein levels in a cell. This posttranscriptional control is particularly relevant for the germ cell lineage, where critical developmental transitions are regulated exclusively at the level of translation. Regulation of translation, in the absence of transcription, is the only form of gene expression that drives mammalian oocyte maturation and early embryo development up to the activation of the zygote genome. Thus, defining how translation is regulated is essential to understand gamete development. In spite of the progress in understanding translational regulation in model organisms, little is known about the molecular details of translational control in mammalian oocytes. We have used a genome-wide approach to determine translation of maternal mRNAs at different stages of maturation in mouse oocytes. Mining of the data has allowed us to identify a novel function for Deleted in azoospermia-like (Dazl), an RNA binding protein (RBP) thought to function mainly during fetal gonadal development. We show that Dazl is indispensable for oocyte progression through the meiotic cell cycle. Using novel strategies to monitor translation in oocytes, we have defined the timing of the major activation of translation and now propose novel mechanisms of activation of translation in oocytes. On the basis of RNA-immunoprecipitation- Chip analysis we propose that Dazl functions as a master regulator of the meiotic cell cycle. On the basis of the above preliminary findings and taking advantage of the genetic models that we have developed, we propose to investigate the mechanisms that control maternal mRNA translation in mouse oocytes. Experiments are organized along three Specific Aims. With the first Specific Aim, we will assemble e a genome-wide map of activation or repression of translation directed by RBPs with functions coordinated by negative and positive feedbacks. These experiments will also determine whether Dazl indeed functions as a master regulator of the meiotic cell cycle. Experiments described in the second Specific Aim will define the mechanisms underlying the burst in translation detected in MI oocytes and its role in meiotic cell cycle progression. The translation of critical components of the cell cycle will be investigated, and the impact of these translations on progression through meiosis will be determined. The third Specific Aim will focus on an additional group of RBPs that likely play an important role in translational repression. We propose to define how Pumilio proteins contribute to translation at the oocyte-to-zyogte transition using a loss-of-function approach. The major outcome of these studies will be an in depth understanding of how networks of RBPs coordinate translation of mRNAs coding for components of the cell cycle as well as proteins necessary for embryo development. These studies are significant for human health, as they will uncover novel regulatory circuits essential for gamete development and likely involved in other critical biological processes such the mitotic cell cycle and embryo development.